Growth Hormone-induced STAT5B Regulates Star Gene Expression Through a Cooperation With cJUN in Mouse MA-10 Leydig Cells

Protein profile analysis of Jilin white goose testicles at different stages of the laying cycle by DIA strategy

BACKGROUND

Jilin white goose is an excellent local breed in China, with a high annual egg production and laying eggs mainly from February to July each year. The testis, as the only organ that can produce sperm, can affect the sexual maturity and fecundity of male animals. Its growth and development are affected and regulated by a variety of factors. Proteomics is generally applied to identify and quantify proteins in cells and tissues in order to understand the physiological or pathological changes that occur in tissues or cells under specific conditions. Currently, the female poultry reproductive system has been extensively studied, while few related studies focusing on the regulatory mechanism of the reproductive system of male poultry have been conducted.

RESULTS

A total of 1753 differentially expressed proteins (DEPs) were generated in which there were 594, 391 and 768 different proteins showing differential expression in three stages, Initial of Laying Cycle (ILC), Peak of Laying Cycle (PLC) and End of Laying Cycle (ELC). Furthermore, bioinformatics was used to analyze the DEPs. Gene ontology (GO) enrichment, Clusters of Orthologous Groups (COG), Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein interaction (PPI) network analysis were adopted. All DEPs were found to be implicated in multiple biological processes and pathways associated with testicular development, such as renin secretion, Lysosomes, SNARE interactions in vesicle trafficking, the p53 signaling pathway and pathways related to metabolism. Additionally, the reliability of transcriptome results was verified by real-time quantitative PCR by selecting the transcript abundance of 6 selected DEPs at the three stages of the laying cycle.

CONCLUSIONS

The funding in this study will provide critical insight into the complex molecular mechanisms and breeding practices underlying the developmental characteristics of testicles in Jilin white goose.

A 35-bp Conserved Region Is Crucial for Insl3 Promoter Activity in Mouse MA-10 Leydig Cells

The peptide hormone insulin-like 3 (INSL3) is produced almost exclusively by Leydig cells of the male gonad. INSL3 has several functions such as fetal testis descent and bone metabolism in adults. Insl3 gene expression in Leydig cells is not hormonally regulated but rather is constitutively expressed. The regulatory region of the Insl3 gene has been described in various species; moreover, functional studies have revealed that the Insl3 promoter is regulated by various transcription factors that include the nuclear receptors AR, NUR77, COUP-TFII, LRH1, and SF1, as well as the Krüppel-like factor KLF6. However, these transcription factors are also found in several tissues that do not express Insl3, indicating that other, yet unidentified factors, must be involved to drive Insl3 expression specifically in Leydig cells. Through a fine functional promoter analysis, we have identified a 35-bp region that is responsible for conferring 70% of the activity of the mouse Insl3 promoter in Leydig cells. All tri- and dinucleotide mutations introduced dramatically reduced Insl3 promoter activity, indicating that the entire 35-bp sequence is required. Nuclear proteins from MA-10 Leydig cells bound specifically to the 35-bp region. The 35-bp sequence contains GC- and GA-rich motifs as well as potential binding elements for members of the CREB, C/EBP, AP1, AP2, and NF-κB families. The Insl3 promoter was indeed activated 2-fold by NF-κB p50 but not by other transcription factors tested. These results help to further define the regulation of Insl3 gene transcription in Leydig cells.

Differential Response of Transcription Factors to Activated Kinases in Steroidogenic and Non-Steroidogenic Cells

Hormone-induced Leydig cell steroidogenesis requires rapid changes in gene expression in response to various hormones, cytokines, and growth factors. These proteins act by binding to their receptors on the surface of Leydig cells leading to activation of multiple intracellular signaling cascades, downstream of which are several kinases, including protein kinase A (PKA), Ca2+/calmodulin-dependent protein kinase I (CAMKI), and extracellular signal-regulated protein kinase 1 and 2 (ERK1/2). These kinases participate in hormone-induced steroidogenesis by phosphorylating numerous proteins including transcription factors leading to increased steroidogenic gene expression. How these various kinases and transcription factors come together to appropriately induce steroidogenic gene expression in response to specific stimuli remains poorly understood. In the present work, we compared the effect of PKA, CAMKI and ERK1/2 on the transactivation potential of 15 transcription factors belonging to 5 distinct families on the activity of the Star gene promoter. We not only validated known cooperation between kinases and transcription factors, but we also identified novel cooperations that have not yet been before reported. Some transcription factors were found to respond to all three kinases, whereas others were only activated by one specific kinase. Differential responses were also observed within a family of transcription factors. The diverse response to kinases provides flexibility to ensure proper genomic response of steroidogenic cells to different stimuli.

COUP-TFII interacts and functionally cooperates with GATA4 to regulate Amhr2 transcription in mouse MA-10 Leydig cells

BACKGROUND

Leydig cells produce testosterone and insulin-like 3, two hormones essential for male sex differentiation and reproductive function. The orphan nuclear receptor COUP-TFII and the zinc finger factor GATA4 are two transcription factors involved in Leydig cell differentiation, gene expression and function.

OBJECTIVES

Several Leydig cell gene promoters contain binding motifs for both GATA factors and nuclear receptors. The goal of present study is to determine whether GATA4 and COUP-TFII cooperate to regulate gene expression in Leydig cells.

MATERIALS AND METHODS

The transcriptomes from GATA4- and COUP-TFII-depleted MA-10 Leydig cells were analyzed using bioinformatic tools. Functional cooperation between GATA4 and COUP-TFII, and other related family members, was assessed by transient transfections in Leydig (MA-10 and MLTC-1) and fibroblast (CV-1) cell lines on several gene promoters. Recruitment of GATA4 and COUP-TFII to gene promoters was investigated by chromatin immunoprecipitation. Co-immunoprecipitation was used to determine whether GATA4 and COUP-TFII interact in MA-10 Leydig cells.

RESULTS

Transcriptomic analyses of GATA4- and COUP-TFII-depleted MA-10 Leydig cells revealed 44 commonly regulated genes including the anti-Müllerian hormone receptor (Amhr2) gene. GATA4 and COUP-TFII independently activated the Amhr2 promoter, and their combination led to a stronger activation. A GC-rich element, located in the proximal Amhr2 promoter was found to be essential for GATA4- and COUP-TFII-dependent activation as well as for the COUP-TFII/GATA4 cooperation. COUP-TFII and GATA4 directly interacted in MA-10 Leydig cell extracts. Chromatin immunoprecipitation revealed that GATA4 and COUP-TFII are recruited to the proximal Amhr2 promoter, which contains binding sites for both factors in addition to the GC-rich element. Cooperation between COUP-TFII and GATA6, but not GATA1 and GATA3, was also observed.

DISCUSSION AND CONCLUSION

Our results establish the importance of a physical and functional cooperation between COUP-TFII/GATA4 in the regulation of gene expression in MA-10 Leydig cells, and more specifically the Amhr2 gene. This article is protected by copyright. All rights reserved.

The Urokinase-Type Plasminogen Activator Contributes to cAMP-Induced Steroidogenesis in MA-10 Leydig Cells

Leydig cells produce androgens which are essential for male sex differentiation and reproductive functions. Steroidogenesis, as well as expression of several genes in Leydig cells, are stimulated by LH/cAMP and repressed by AMP/AMPK. One of those genes is Plau, which codes for the urokinase-type plasminogen activator (uPA), a secreted serine protease. The role of uPA and the regulation of Plau expression in Leydig cells remain unknown. Using siRNA-mediated knockdown, uPA was required for maximal cAMP-induced STAR and steroid hormone production in MA-10 Leydig cells. Analysis of Plau mRNA levels and promoter activity revealed that its expression is strongly induced by cAMP; this induction is blunted by AMPK. The cAMP-responsive region was located, in part, in the proximal Plau promoter that contains a species-conserved GC box at −56 bp. The transcription factor Krüppel-like factor 6 (KLF6) activated the Plau promoter. Mutation of the GC box at −56 bp abolished KLF6-mediated activation and significantly reduced cAMP-induced Plau promoter activity. These data define a role for uPA in Leydig cell steroidogenesis and provide insights into the regulation of Plau gene expression in these cells.

Transcription Factors in the Regulation of Leydig Cell Gene Expression and Function

Cell differentiation and acquisition of specialized functions are inherent steps in events that lead to normal tissue development and function. These processes require accurate temporal, tissue, and cell-specific activation or repression of gene transcription. This is achieved by complex interactions between transcription factors that form a unique combinatorial code in each specialized cell type and in response to different physiological signals. Transcription factors typically act by binding to short, nucleotide-specific DNA sequences located in the promoter region of target genes. In males, Leydig cells play a crucial role in sex differentiation, health, and reproductive function from embryonic life to adulthood. To better understand the molecular mechanisms regulating Leydig cell differentiation and function, several transcription factors important to Leydig cells have been identified, including some previously unknown to this specialized cell type. This mini review summarizes the current knowledge on transcription factors in fetal and adult Leydig cells, describing their roles and mechanisms of action.